Magnetic material and magnet core



mmmm, CROSSREFERENEEJ Exa comma OR PLASTC mm;

Feb. 16, 1932. w, ANDREWS ET AL 1,845,113

MAGNETIC MATERIAL AND MAGNET CORE Filed Dec. 31. 1927 WWW/1M PatentedFeb. 16, 1932 Human STATES JOHN WENDELL ANDREWS, OF CHICAGO,

ASSIGNORS TO WESTERN ELECTRIC COMPANY, INCORPORATED,

A CORPORATION OF NEW YORK am) RANDALL GILLIS, or 131mm, rumors,

OF NEW YORK, N. Y,

MAGNETIC MATERIAL AND MAGNET CORE Application filed December 81, 1927.Serial 1T0. 244,020.

This invention relates to magnetic materials and magnet cores, andespecially to magnetic cores for loading coils for use in telephonecircuits. j The principal object of the invention is the production. ofmagnetic elements hav ng stab e magnetic properties undel: varyingmagnetic conditions. a

Another object of the invention is the production of magnetic elementshaving low core losses and a relatively high permeability to enable agiven inductance "to be obtained from a minimum amount of material, andpossessing to a high degree those electrical f and magneticcharacteristics which make 11:

highly desirable in electrical signalling apparatus, particularly inloading coils for telephone circuits. I Y Y In accordance with oneembodiment, the present invention contemplates the construc-' tion ofmagnetic cores of an allo including nickel and iron in finely dividediorm, heat treated to -Ha'r e a higher inherent magnetic permeabilityand lower inherent hysteresis 26 loss'tha n iron, and combined with asuitable insulatin material. More specifically, the

: mates the formation of magnetic cores of a n'ckel-iron allo in finelydivided form in whlcli the proportions of its :0 constituents are .suchthat the resulting alloy has tlhe maiiimum magneltic stabilit The metapartic es are treate with a re ractory insulating material whereby the a0y particles are individually insulated after which they are compressedinto cores of the desired sha e and size.) The cores are heat tr ateglat t e optimum temperature for the paftid lar alloy of which they areconstructed to give the cores'the' desired mechanical, elec- 40 tricaland magnetic characteristics.

It is believed that the mvention will be clearly understood from thefollowing detailed description of one embodimentthereof and theaccompanying drawings, which Fig. 1 is a perspective view of a sectionof a loading coil core. made in accordance with the present invention,and

Fig. 2 shows a plurality of these sections assembled to form a completedcore.-

It will be understood, however, that this is merely illustrative and theinvention is not limited to the production of this form of core, but isadapted to the production of cores for magnetic articles of many forms.

In carrying out the present invention the ma netic material is preparedin the followmg manner. e magnetic material employed is pre ared from anickel-iron alloE commonly re erred to as erma o w 10 is treated in amanner more u y described in the copending application of H. M. E.Heinicke, Serial No. 229,801, filed October 29, 1927, to reduce thealloy to a finely divided form. Experience has proven that where loweddy current losses are desired it is essential that the particles be ofa small size and preferably 0 such size that all of the particles willreadily pass through what is generally known as a 120 mesh screen and alarge percentage pass through a 200 mesh screen. According to oneembodiment of the invention, the alloy is prepared by melting aproximately 80 parts of nickel and 20 parts 0 iron in an oxidizingatmosphere and pouring the resulting alloy into a mold. When preparedaccording to the 'foregoin process,'the resulting alloy will beexceedingly brittle and it is therefore particularly adapted to bereduced-to a finely divided or dust form from which cores may be molded.

The brittle ingots obtained from the above described process aresuccessively passed through progressively reducing hot rolls whichdecrease the cross sectional dimensions of the piece of material and thefinal roll is effected at approximately the temperature at which thealloy ceases to be malleable, after which the rolled material isquenched to a temperature below that at which it loses its malleability.By the hot rolling and quenching process the size of the crystallinestructure is materially reduced, which is very de I sirable becausedisintegration of the material takes place mainly at the crystalboundaries, and consequently the smaller the size of the crystals thefiner the dust which can be produced from the finished product. Therolled and quenched material is broken into 'shortpieces and thepiecesare crushed in a jaw crusher, hammer mill, or any other suitscam PlAS 'Cable type of apparatus, after which .the crushed material is reduced toa fine dust in a ball mill or any other suitable p'ulverizing device.The dust is sieved through a 120 5 mesh sieve and any residue-isremelted and again carried through the above described operations toreduce the material to a finely divided form. The finel 1 tained by t eabove described operations is particularly adapted to be formed intorings or cores for loading coils by individuallyinsulating the particleswith a refractory insulating material and ,compressing the.

insulated particles. The particles ma be insulated in accordance withthe metho described more fully in our copending applicain which methodthe finely divided particles of the nickel-iron alloy are annealed in aclosed container at a temperature of approximately 925 (1, after whichthe resulting cake of annealed alloy is again reduced to a finely ividedform. The annealed then individually insu ate articles are w1t1 arefrac- A tory insulator comprising approximately:

- parts of chromic acid 5 parts of ta 0 4 parts of water lass composedof 50% so 2 total solids an con alning approximately 1.58 parts of SiOto 1 part of Na O.

The insulated dust particles are then in a form suitable for ressinginto cores or rings 35 which are prefera ly formed with a pressure ofapproximately 200,000 pounds. per. square inch. A hi hpressure is usedin forming the rings in 5? er toiaatase their density, since it has beenfound that the'permeability of the 40 rings increases with increaseddensity. Following this step, the cores are transferred without undulyexposing them to the air into an annealing furnace in which they areannealed at the optimum annealing temperature of approximately Q. andcooled. If

"he i1 d..ia-ua r.

necessary, the cores may M a to remove soluble substances and to renderthe cores chemically stable, and dried at a temperature of approximately100 C.

A plurality of rings thus romaine then stacked coaxially to form a coreon which the usual toroidal winding is applied, the number of suchringsfu'sed depending upon the existing electrical characteristics ofthe telephone circuit with which the loading coils are to be associated.

Although the alloy "has been des'cribed asing composed of approximately80% nickel and the remainder principally iron, 50 it is to be understoodthat the proportions of the ingredients may be varied without departinfrom the spirit and scope of the invention. For example, nickel-ironallo having substantially stable magnetic properties may be produced byemploying from divided magnetic material obposed of the oxides of theconstituents of the tion, Serial No. 102,729, filed April 17, 1926,

LAQQIHIIV alloy upon the particles. In fact, any insulating materialwhich will serve to individually insulate the finely divided particlesand which will withstand the effects of the annealing treatment to whichthe compressed rings are subjected may be employed with. satisfactoryresults. a

By the term magnetic stability which is employed hereinbefore in thespecification and hereinafter in the annexed claims, is meant that thepermeability of the material and consequently the inductance of a' coilemploying such material is substantially unaffected by instantaneousdirect current magnetizations. The magnetic stability of the alloy maybe computed from the diflerence in the inductance of a coil before andafter being subjected to an instantaneous direct current magnetization,and may be expressed "by the following formula:

100AL L .JOOAL which represents the percent change in inductanceproduced by the instantaneous direct current magnetization, falls withinthe limits of i.5% andconsequently the magnetic stability, representedby the letter for an alloy containing approximately nickel is 99.5% to100.5%.

B using an alloy of the proportions stated in t e preceding paragraphsand by followingi the foregoing method of insulating the ividual alloyparticles and compressing the particles into cores or rings, magneticstructures are produced which have an extremely *high magnetic stabilityand permeability from the minimum amount of material. By the use of suchcores or rin s, inductance units having a high magnetic stability,having the same permeability with What is claimed is:

1. A magnetic core of high magnetic stability composed of finely dividedindividually insulated particles of an alloy of approximately 80% nickeland iron annealed at a temperature of approximately 925 C. formed intoshape under a pressure of approximately 200,000 pounds per square I inchand annealed as a whole at a tempera-' ture of approximately 500 C.

2. The process of manufacturing ma netic cores of high magneticstability whic consists in reduclng an alloy of approximately 80% nickeland 20% iron to dust, annealing the dust at a temperature of aproximately 925 C., reducing the anneale cake to dust a ain, coating theparticles of dust with a re ractory insulating material, pressing theinsulated dust into form under a pressure of approximately 200,000pounds per square inch, and annealing the formed cores at a temperatureof approximately 3. A magnetic core of high ma etic stability comprisingfinely divided in ividually insulated particles of an alloy comprisingfrom 79% to 84% nickel and the remainder principally iron annealed at atemperature of the order of 925 0. formed into shape under a pressure ofthe order of 200,- 000 pounds per square inch and annealed as a .wholeto produce a high magnetic stability. In witness whereof, we hereuntosubscribe our7names this 24th day of December, A. D. 192

JOHN WENDELL ANDREWS. RANDALL GILLIS.

